Protesters in Adelaide have pelted a man dressed as Prime Minister Kevin Rudd with their shoes as part of nationwide protests against the Federal Government's emissions targets.

The protest on the steps of South Australia's Parliament house was in opposition to the Government's 5 per cent emissions reduction target set yesterday.

After hearing from Greens Senator Sarah Hanson-Young and State MP Mark Parnell, the man pretending to be the Prime Minister was invited to the microphone, and protesters threw their shoes at him.

Earlier Senator Hanson-Young told the crowd there was little difference between Mr Rudd and former prime minister John Howard.

"What an embarrassment that Australia is only prepared to cut carbon emissions by 5 per cent," she said.

"Who would have thought that this was coming from a Rudd Labor Government who won their election based on the fact that they were going to be the party that took action on climate change."

Meanwhile in Sydney at least 80 people have gathered outside the Federal Government's offices in the CBD.

They say 5 per cent is as good as nothing and are calling for a cut of a least 25 per cent.

The New South Wales Greens MP, Jon Kaye, has told one of the protests in Sydney that Mr Rudd's honeymoon is over.

"Five per cent or nothing makes not a big amount of difference. What we really need is 25 per cent or better still, 40 per cent so Australia can not only participate in reducing global emissions but also build a strong renewable energy industry," he said.

Nicky Isom, from the Australian Student Environmental Network, has told the activists in Sydney that the Prime Minister was elected in the hope he would lead the world on climate change.

"Yesterday, Rudd stepped into Howard's shoes and became the new spokesperson for the greenhouse mafia in Australia," he said.

"He announced pathetic 5 per cent reduction targets, not based on science, not based on equity, not based on evidence. Rudd declared the honeymoon over."

Environmentalists are also protesting outside the offices of federal Labor MPs in capital cities and regional centres across Australia.